The present invention relates to a change gear unit, and more particularly, to a motor vehicle change gear unit in which an output shaft can, in each case, be moved optionally into a drive connection with a parallel input shaft, by at least three gear wheel stages to form forward gears and by one gear wheel stage to form a reverse gear. An input-side gear unit element of a three-element differential gear unit of the planetary gear type is arranged, with the central axis of the said gear unit element, parallel to the input shaft and output shaft, by way of two gear wheel stages, and the two output-side gear unit elements of the differential gear unit which are centrally arranged to the central axis can each be coupled to a vehicle wheel of a drive axle.
More specifically in the change gear unit the two input-side gear wheels of two gear wheel stages which are used to form forward gears as a drive connection between the input shaft and the output shaft, and the input-side gear wheel of the gear wheel stage which is used to form the reverse gear as a drive connection between the input shaft and output shaft are each arranged rotationally fixed relative to the input shaft. An intermediate gear wheel which is independently rotatably mounted can be moved into meshing engagement both with the input-side and with the output-side gear wheel of the gear wheel stage which is used to form the reverse gear as a drive connection between the input shaft and output shaft.
In a known change gear unit as described in EP 0 242 338 B1, two gear wheel stages are used to form forward gears and one gear wheel stage is used to form a reverse gear, in each case as a drive connection between the input shaft and output shaft. A clutch sliding sleeve is arranged axially displaceably and rotationally fixed with respect to the output shaft, for optionally engaging the two gear wheel stages in order to form forward gears. The sliding sleeve is additionally provided with continuous toothing for use as an output-side gear wheel of the gear wheel stage in order to form the reverse gear. This gear wheel stage acts as a drive connection in that the sliding sleeve is moved into its axial neutral position and the intermediate gear wheel is then pushed into the continuous toothings of the gear-shift sliding sleeve and of the associated input-side gear wheel on the input shaft. Synchronization of the reverse gear is thus not provided.
In the known change gear unit, the output shaft can be moved into a drive connection with the differential gear unit by two gear wheel stages which can be optionally engaged. In total, thereby, four forward gears are obtained in conjunction with the two other gear wheel stages.
In the known change gear unit, the objective was to reduce the gear wheel stages in comparison with a four-gear change gear unit in which one gear wheel stage is provided for each forward gear, i.e. a total of four gear wheel stages, between the input shaft and output shaft. The two input-side gear wheels of the forward-gear gear wheel stages were keyed onto the input shaft. It was also known that a third gear wheel stage might form forward gears as a drive connection between the input shaft and output shaft so that a six-speed gear unit is obtained, but the way to obtain a six-speed gear unit has not been described in the prior art.
In the change gear unit described in CH-PS 205 282, the input-side gear wheels of the gear wheel stages, which are used to form the forward gears II to V as a drive connection between the input shaft and output shaft are rotatably seated, as loose wheels, on the input shaft, in order to form the lowest forward gear I and the reverse gear. In each case, a particular input gear wheel arranged rotationally fixed on the input shaft and a common output gear wheel having three crown gears and seated loosely on the output shaft as a sliding gear wheel were provided for the gear wheel stages. One of the three crown gears was optionally moved into a meshing engagement with the associated input gear wheels. One of the two other crown gears was in a meshing engagement with one and the same gear wheel assigned to the differential gear unit and at the same time arranged concentrically with respect to its central axis and fixed in terms of movement with respect to its input-side gear unit element. The output gear wheel with the three crown gears and the output gear wheel which was associated with the gear wheel stage in order to form the forward gear V with the lowest transmission ratio were arranged both at opposite ends of the output shaft and in change gear unit casing chambers separated from one another by an intermediate casing wall.
In another known change gear unit as described in DE 30 37 990 A1, two input shafts, which are concentric with respect to one another, are movable into a drive connection with a parallel output shaft by, on one hand, one power shift clutch with a drive motor and, on the other hand, by gear wheel stages, in order to form forward gears and one reverse gear. The gear wheel stages and their shifting apparatuses were activated using a shift drum which is driven by an electric motor.
Finally, yet another change gear unit was described in DE 41 26 161 C2. The axes of rotation of one input shaft and one output shaft and the central axis of a differential gear unit were arranged both parallel to one another and in a main plane of a gear unit casing. The gear unit casing was divided, in a dividing plane which is located perpendicular to the axes of rotation, into a gear wheel casing which accommodated all the gear wheel stages for forming the gear unit speeds and partially accommodated the differential gear unit, and into an adaptor casing which completely accommodates a separating or starting clutch and partially accommodates the differential gear unit. Seated both on the input shaft and on the output shaft were loose wheels of gear wheel stages for forming forward gears which were activated via three shift rods located parallel to one another and also to the transmission shafts and are arranged on one side of the main plane. On the other side of the main plane, a bearing bolt for the rotatable bearing of intermediate gear wheels of a gear wheel stage was arranged parallel to the input shaft in order to form the reverse gear. The bearing bolt could be inserted by one end into a receptacle hole of the gear wheel casing and by its other end into a receptacle hole of the adaptor casing. The receptacle hole of the adaptor casing opened in a dividing surface located in the dividing plane.
An object of the present invention is to use as few different types of parts as possible while providing a change gear unit which has at least five forward gears and one synchronized reverse gear.
This object has been advantageously achieved in accordance with the present invention by providing that the intermediate gear wheel is arranged to mesh continuously with the input-side gear wheel, which is rotationally fixed with respect to the input shaft, of the gear wheel stage having the largest transmission ratio of three gear wheel stages whose transmission ratios form a succession and which forms the forward gears as the drive connection between the input shaft and the output shaft. The output-side gear wheel of the gear wheel stage forms the reverse gear as a drive connection between the input shaft and the output shaft. The two output-side gear wheels of that gear wheel stage having the smallest transmission ratio of the three gear wheel stages whose transmission ratios form the succession and which form forward gears as a drive connection between the input shaft and the output shaft, and of the gear wheel stage which forms the reverse gear as a drive connection between the input shaft and the output shaft, are arranged rotatably and axially adjacent to one another on the output shaft and are coupleable to the output shaft.
In the change gear unit according to the present invention, the reverse gear is synchronized, and a particular input-side gear wheel for the gear wheel stage for forming the reverse gear is dispensed with. The input shaft can be manufactured in one piece with the three gear wheels of the gear wheel stages in order to form five or six forward gears. In one embodiment of the present invention, these three gear wheel stages require, together with the gear wheel stage forming the reverse gear, only two clutches for the respective engagement, as a drive connection between the input shaft and output shaft.
In another embodiment of the gear change unit according to the present invention, all the gear wheels of the input shaft can be manufactured with the gear-cutting method by providing, inter alia, that the output-side gear wheel of the gear wheel stage having the smallest transmission ratio of the three gear wheel stages, whose transmission ratios form a succession and form the forward gears as a drive connection between the input shaft and the output shaft, is arranged axially between the output-side gear wheel of the gear wheel stage which forms the reverse gear as a drive connection between the input shaft and the output shaft, and also between the input-side gear wheels of the gear wheel stages constituting a drive connection between the output shaft and the differential gear unit.
According to another advantageous feature of the present invention, the change gear unit can be extended to seven or eight forward gears while maintaining the advantages of the five-gear or six-gear embodiment.
An advantageous activation of the clutches of the change gear unit according to the present invention can be achieved by providing that, for example, the clutches operatively associated with the gear wheel stages constituting the drive connection between the input shaft and the output shaft, and the clutches operatively associated with the gear wheel stages constituting the drive connection between the output shaft and differential gear unit, are arranged to be activated by a shift drum having a respective shift fork.
An advantageous refinement of a gear unit casing of the change gear unit according to the present invention is achievable in that a first casing plane of a gear unit casing contains axes of rotation of the input shaft and the output shaft, a second casing plane of the gear unit casing contains an axis of rotation of the output shaft and the central axis of the differential gear unit, and a third casing plane located between the first and second casing planes, contains the axis of rotation of the output shaft and the geometric axis of a bearing axle, and the shift forks are arranged to be axially displaceable with respect to the associated transmission shaft, with an intermediate connection of the bearing axle.